The Shell Rock

This is the rock I was talking about in my previous post. Imagine walking along and you see a rock and pick it up. It looks like sandstone, and there are shell impressions on the outside.

Then it falls open in your hand, and you see a shell impression and a shell cast where the rock exactly fits together, but no shell! Where did it go? I think it must have been dissolved by the water that flowed through the sandstone. Maybe the water was acidic, like acid rain is today, and ate away the carbonate shell. Just my speculation.

Can you see the bump and the hollow place? I wish I had put arrows on this picture, but you probably can see it if you look carefully. - Auriel Ragmon

P.S., I added a couple of pictures to the "Little Rock" post, if you would like to see the Mima Mounds and the Tenino Museum Building. AR